Spatial variation in the sensitivity of freshwater macroinvertebrate assemblages to chemical stressors

Spatial variation in the recovery potential of freshwater macroinvertebrate assemblages: Moving towards spatially defined assemblage vulnerability to chemicals

The vulnerability of freshwater biodiversity to chemical stressors is dependent on its ability to resist chemical stress and recover from any stress-induced effects. Spatial variation in recovery has the potential to exacerbate or mitigate assemblage vulnerability but this has not been explored in detail. By combining information on assemblage-specific recovery potential with information on assemblage-specific chemical sensitivity, we have demonstrated that the vulnerability of 3307 macroinvertebrate assemblages to 18 different chemicals is spatially dependent and that recovery potential may reduce chemical risk. The recovery potential of each assemblage was quantified based on trait information and landscape factors using a weighted sum method, but it did not consider succession processes. Recovery potential varied by river type with assemblages in mid-altitude siliceous rivers with small catchments in the west of England having the lowest recovery potential. For 17 or the 18 chemicals investigated, there was a positive correlation between the recovery potential and sensitivity and this was strongest for assemblages exposed to metals. More sensitive assemblages had a higher recovery potential and were therefore potentially less vulnerable than would be expected based on sensitivity alone. Assemblages in rivers with small catchments were the most vulnerable to chemical exposure. Furthermore, assemblages with high vulnerability to insecticide exposure were more prevalent in mid-altitude rivers with siliceous geology in the west of England, whereas assemblages with high vulnerability to metals were more prevalent in lowland rivers with calcareous or mixed geology in the midlands. This study: (i) highlights the importance of spatial context in determining the risk of chemical pollution to freshwater biodiversity; (ii) demonstrates how spatial variation in taxonomic composition influences both the internal and external recovery of assemblages and how landscape factors modify trait-based recovery capabilities; (iii) provides the foundations for spatially-defined vulnerability assessment by identifying ecological scenarios for assessing chemical risk.